Vergleich von Wettermodellen für Konolfingen

The blue lines correspond to the forecasts computed by different high-resolution weather models. Also shown are the members of a traditional ensemble prediction, where the same weather model (GFS) is run several times with slightly different initial conditions, to reflect uncertainties in the observations required to run a forecast model. The GFS members have been downscaled and bias corrected to match local weather conditions, data from the high-resolution models is untouched.

In the top graph, the temperature forecast for Konolfingen is shown using light blue for different high-resolution models and red for the GFS ensemble members. The black line represents the mean of all forecasts and the dashed line the meteoblue consensus forecast as shown in our weather forecasts.

The 2nd graph shows the accumulated precipitation forecast, that is the total amount that falls from today up to the date shown on the time axis. Purple colour is used to indicate times where precipitation is falling.

The 3rd graph is forecast cloud cover in percent using light blue for the high-resolution weather models and green for the GFS ensemble members.

The 4th graph indicates the wind forecast as computed by high resolution models (light blue) and by the ensemble prediction (green). Also shown is the daily wind direction summary in form of a wind rose. Larger segments indicate that this wind direction is more likely and more frequent over the day than directions having smaller segments. If you have many segments of all about equal size than the forecast of wind direction is very uncertain. If there are predominantly two opposing directions this often indicates a thermal wind circulation where wind blows from a different direction during the day than at night.

Why do we show a traditional ensemble forecast and a multi model forecast at the same time?

A traditional ensemble (e.g. GFS) computed with the same forecast model often underestimates the uncertainties in the weather for the first 3 to 5 days thus overestimating the confidence in the forecast. Furthermore, the traditional ensemble is run at much lower resolution, thus neglecting some of the local weather phenomenon, which can be seen in high resolution models. It is very important to note, that all members of a traditional ensemble have the same likelihood of being true (there is no way to tell in advance which one will be better). This contrasts with the high-resolution models, where some deliver better forecasts than others depending on the location and weather conditions.